VR Tubes

These are a mix of different VR tubes used in tube power supplies. VR stands for Voltage Regulator. They used to be used (and still are in some circles) where zener diodes would be used now. In a tube-based power supply, they create a stable reference voltage that can be used to stabilize an output voltage using a feedback loop.

The basic principle is common to all neon (and other noble gas) glow discharge tubes: When the tube is glowing, the voltage at the anode is fairly stable and is defined by the characteristics of the tube, not by the voltage that was used to ignite it. Nixie tubes typically have a maintenance voltage of around 130-150V. The tubes here have a range of voltages chosen for specific applications. The designator specifies maintenance voltage, but different manufacturers used different mixtures of noble gases to get these.